The present invention relates to a method of measuring the tear resistance of paper as well as to an apparatus for applying the method.
At present, the tear resistance of paper samples is determined in separate air-conditioned laboratory rooms. The actual determination is generally effected by means of a tear resistance measuring device operating on standardized pendulum principle. A sample is manually cut into precision measured packs of dimension sample blanks, comprising four sheets on top of each other and being manually fixed by means of clamping screws in a measuring device. The fixed pack of sample blanks is torn at precise length by means of potential energy of a pendulum. The effort required for tearing is determined as the reduction of potential energy possessed by said pendulum. Tear resistance can now be calculated on the basis of a given formula.
The present day methods and assemblies for carrying out tear resistance measurements involve drawbacks leading to inaccurate and deficient results in view of practical conditions. When today's measuring methods are employed, the sample blanks are cut out and fixed manually. During the treatment, the properties of a sample may change from original (e.g. moisture). Performing the measuring requires staff trained for the job and measurements should be effected in an airconditioned laboratory room. Furthermore, the measuring results always depend to some extent on a person doing the job. This drawback is due to the manner and ability characteristic of a person doing the measuring to cut out, fix and handle a sample blank as well as to the manner and ability to observe and read the analogous measuring results at the moment of measurement.
When the properties of paper are being tested, the aim is to apply the test results for the control of production processes or for watching the application properties. When using the available methods and devices, there is always a substantial time lapse between sampling and measuring events, during which the properties of a sample may alter and measuring results cannot be used immediately after the sampling. At present, the tear resistance is determined by tearing a pack of sample blanks comprising a plurality of sheets on top of each other. In the working conditions, however, it is essential to know the behavior of an individual sheet of paper which is why the available methods and devices are insufficient.
When using the available methods, a pack of sample blanks is torn by means of a pendulum and the effort required by tearing is determined as reduction of the potential energy of said pendulum. During the tear measuring, the strength of a force keeping up the tearing is not monitored, nor can the tearing rate be adjusted. Furthermore, a pendulum produces an increasing tearing force, the accurate strength of a force required for tearing being difficult to measure.
An object of the invention is to provide a method for determination of the tear resistance of paper in order to eliminate drawbacks of the available methods. A particular object of the invention is to provide a method utilized for testing a single layer paper in a manner that tearing rate can be adjusted. Another object of the invention is to provide a method, wherein paper is torn at a constant rate while continuously monitoring the level of tearing force. A still further object of the invention is to provide an apparatus for applying the method, the use of said apparatus eliminating some of the handling of a paper sample earlier necessary and said apparatus facilitating the immediate availability of measured results. An object of the invention is also to provide an apparatus for automatically handling, tearing and determining the tear resistance of paper.
The object of this invention is achieved by means of a method and apparatus substantially characterized by what has been set forth in the annexed claims.